The requirement for reliability of transmission in a Wavelength Division Multiplexing (WDM) long-distance transmission network is very high, and thus various protection techniques of the optical path level and the optical multiplexing level are generally used so that a service transmitted on an active line can be switch to a protection line (i.e., a standby line) via a protection apparatus when an abnormal failure occurs in a normal active line, such as, fiber breaking caused by construction and so on, thereby not affecting users' use as far as possible.
In various optical transmission systems, the protection system is generally divided into two categories: optical layer protection and circuit layer protection, wherein optical layer protection mainly achieves to switch an optical path via various optical devices, and makes use of a standby optical path to substitute an active line where a fault occurs for transmitting service, thereby achieving the purpose of protecting user's service. Currently, the main protection modes often applied by optical layer protection are a linear 1+1 protection mode and a linear 1:1 protection mode, wherein:
in a 1+1 protection mode, a standby line is reserved for each active line, and a service transmitted on an active line can be timely switched onto a standby line for transmission when a fault occurs in the active line. This protection mode has a simple structure and works efficiently and reliably. However, the 1+1 protection mode also has a plurality of inherent deficiencies at the same time, that is, it needs to reserve a standby line for an active line, and the a standby line is required to be in an available state whenever necessary and cannot transmit other additional services due to its protection feature, thereby causing wastes of bandwidth resources and a very low utilization ratio of the bandwidth.
In a 1:1 protection mode, a standby line is reserved for an active line, but it is different from a 1+1 protection mode, and since additional services can be transmitted in a standby line in 1:1 protection, wastes of bandwidths are reduced to some extent. However, in 1:1 protection, when a fault occurs in an active line, it needs to interrupt an additional service transmitted on a standby line and switch a service transmitted on the active line to the standby line for transmission, which gives rise to the delay or loss of the service transmitted on the standby line and the lower success rate of service transmission, thereby affecting transmission performance of the whole system and user's use feeling to service.
In practical applications, it often needs to use different protection modes according to different features of services to be transmitted, for example, as for a service having a high requirement for the service transmission success rate, it is hoped that a 1+1 protection mode is used so as to ensure the success rate of service transmission; as for a service having a low requirement for the service success rate, it is hoped that a 1:1 protection mode is used so as to improve the utilization rate of bandwidth. To sum up, currently a protection mode applied in an optical transmission system is stationary, that is, either a 1+1 protection mode or a 1:1 protection mode is used, and it is impossible to select a protection mode according to different features of services to be transmitted, resulting in a problem that transmission requirements of service cannot be satisfied.